I assume an expensive, recently-on-the-market fixed-gear bike has a pretty good headset. So I don't know why it's gone south so soon. But if you're collecting enough water in your frame to slosh noticably, I'm assuming you ride a fair bit in fairly crappy weather. Did you do the same with your previous bike?
I almost always put a lizard skins neoprane headset cover on the bottom headset race of my bikes, especially the ones without fenders. Works well, adds next-to-zero drag. See
http://www.performancebike.com/shop/...4&item=00-7332 for example.